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AdeIJK, a resistance-nodulation-cell division pump effluxing multiple antibiotics in Acinetobacter baumannii.

ABSTRACT: We have identified a second resistance-nodulation-cell division (RND)-type efflux pump, AdeIJK, in clinical isolate Acinetobacter baumannii BM4454. The adeI, adeJ, and adeK genes encode, respectively, the membrane fusion, RND, and outer membrane components of the pump. AdeJ belongs to the AcrB protein family (57% identity with AcrB from Escherichia coli). mRNA analysis by Northern blotting and reverse transcription-PCR indicated that the genes were cotranscribed. Overexpression of the cloned adeIJK operon was toxic in both E. coli and Acinetobacter. The adeIJK genes were detected in all of the 60 strains of A. baumannii tested. The two latter observations suggest that the AdeIJK complex might contribute to intrinsic but not to acquired antibiotic resistance in Acinetobacter. To characterize the substrate specificity of the pump, we have constructed derivatives of BM4454 in which adeIJK (strain BM4579), adeABC (strain BM4561), or both groups of genes (strain BM4652) were inactivated by deletion-insertion. Determination of the antibiotic susceptibility of these strains and of BM4652 and BM4579, in which the adeIJK operon was provided in trans, indicated that the AdeIJK pump contributes to resistance to beta-lactams, chloramphenicol, tetracycline, erythromycin, lincosamides, fluoroquinolones, fusidic acid, novobiocin, rifampin, trimethoprim, acridine, safranin, pyronine, and sodium dodecyl sulfate. The chemical structure of these molecules suggests that amphiphilic compounds are the preferred substrates. The AdeABC and AdeIJK efflux systems contributed in a more than additive fashion to tigecycline resistance.

SUBMITTER: Damier-Piolle L

PROVIDER: S-EPMC2224764 | biostudies-literature | 2008 Feb

REPOSITORIES: biostudies-literature

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AdeIJK, a resistance-nodulation-cell division pump effluxing multiple antibiotics in Acinetobacter baumannii.

Damier-Piolle Laurence L Magnet Sophie S Brémont Sylvie S Lambert Thierry T Courvalin Patrice P

Antimicrobial agents and chemotherapy 20071217 2

We have identified a second resistance-nodulation-cell division (RND)-type efflux pump, AdeIJK, in clinical isolate Acinetobacter baumannii BM4454. The adeI, adeJ, and adeK genes encode, respectively, the membrane fusion, RND, and outer membrane components of the pump. AdeJ belongs to the AcrB protein family (57% identity with AcrB from Escherichia coli). mRNA analysis by Northern blotting and reverse transcription-PCR indicated that the genes were cotranscribed. Overexpression of the cloned ade ...[more]

PMID: 18086852

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Project description:Acinetobacter baumannii is a nosocomial pathogen of increasing importance due to its multiple resistance to antibiotics and ability to survive in the hospital environment linked to its capacity to form biofilms. To fully characterize the contribution of AdeABC, AdeFGH, and AdeIJK resistance-nodulation-cell division (RND)-type efflux systems to acquired and intrinsic resistance, we constructed, from an entirely sequenced susceptible A. baumannii strain, a set of isogenic mutants overexpressing each system following introduction of a point mutation in their cognate regulator or a deletion for the pump by allelic replacement. Pairwise comparison of every derivative with the parental strain indicated that AdeABC and AdeFGH are tightly regulated and contribute to acquisition of antibiotic resistance when overproduced. AdeABC had a broad substrate range, including β-lactams, fluoroquinolones, tetracyclines-tigecycline, macrolides-lincosamides, and chloramphenicol, and conferred clinical resistance to aminoglycosides. Importantly, when combined with enzymatic resistance to carbapenems and aminoglycosides, this pump contributed in a synergistic fashion to the level of resistance of the host. In contrast, AdeIJK was expressed constitutively and was responsible for intrinsic resistance to the same major drug classes as AdeABC as well as antifolates and fusidic acid. Surprisingly, overproduction of AdeABC and AdeIJK altered bacterial membrane composition, resulting in decreased biofilm formation but not motility. Natural transformation and plasmid transfer were diminished in recipients overproducing AdeABC. It thus appears that alteration in the expression of efflux systems leads to multiple changes in the relationship between the host and its environment, in addition to antibiotic resistance. Increased expression of chromosomal genes for RND-type efflux systems plays a major role in bacterial multidrug resistance. Acinetobacter baumannii has recently emerged as an important human pathogen responsible for epidemics of hospital-acquired infections. Besides its remarkable ability to horizontally acquire resistance determinants, it has a broad intrinsic resistance due to low membrane permeability, endogenous resistance genes, and antibiotic efflux. The study of isogenic mutants from a susceptible A. baumannii clinical isolate overproducing or deleted for each of the three major RND-type pumps demonstrated their major contribution to intrinsic resistance and to the synergism between overproduction of an efflux system and acquisition of a resistance gene. We have also shown that modulation of expression of the structural genes for the efflux systems results in numerous alterations in membrane-associated cellular functions, in particular, in a decrease in biofilm formation and resistance gene acquisition.

Project description:Overexpression of chromosomal resistance-nodulation-cell division (RND)-type efflux systems with broad substrate specificity contributes to multidrug resistance (MDR) in Acinetobacter baumannii We have shown that modulation of expression of the structural genes for the efflux systems AdeABC and AdeIJK confers MDR and results in numerous alterations of membrane-associated cellular functions, in particular biofilm formation. However, the contribution of these RND pumps to cell fitness and virulence has not yet been studied. The biological cost of an antibiotic resistance mechanism is a key parameter in determining its stability and dissemination. From an entirely sequenced susceptible clinical isolate, we have generated a set of isogenic derivatives having single point mutations resulting in overexpression of each efflux system or with every pump deleted by allelic replacement. We found that overproduction of the pumps results in a significant decrease in fitness of the bacterial host when measured by competition experiments in vitro Fitness and virulence were also evaluated in vivo both in systemic and pulmonary infection models in immunocompetent mice. A diminished competitiveness of the AdeABC-overexpressing mutant was observed only after intraperitoneal inoculation, but not after intranasal inoculation, the latter mimicking the most frequent type of human A. baumannii infection. However, in mice infected intranasally, this mutant was more virulent and stimulated an enhanced neutrophil activation in the lungs. Altogether, these data account for the observation that adeABC overexpression is common in MDR A. baumannii frequently found in ventilator-associated pneumonia.Overproduction of the RND AdeABC efflux system is observed with a high incidence in multidrug-resistant Acinetobacter baumannii and results in increased resistance to several antibiotics of choice for the treatment of infections caused by this nosocomial pathogen. It was therefore important to study the biological cost of the overexpression of the adeABC structural operon which is normally tightly regulated. Fitness diminution of an overexpressing mutant detected in vitro and in vivo in a model that mimics sepsis was not observed in a pulmonary infection model in which the mutant was more virulent. This points out that increased virulence can occur independently from prolonged persistence in the infected organ and can account for the elevated incidence of this resistance mechanism in clinical isolates. The study also indicates that transposon libraries will identify only virulence genes that are expressed under physiological conditions but not those that are tightly regulated.

Project description:Genetic alterations leading to the constitutive upregulation of specific efflux pumps contribute to antibacterial resistance in multidrug resistant bacteria. The identification of such resistance markers remains one of the most challenging tasks of genome-level resistance predictors. In this study, 487 non-redundant genetic events were identified in upstream zones of three operons coding for resistance-nodulation-division (RND) efflux pumps of 4,130 Acinetobacter baumannii isolates. These events included insertion sequences, small indels, and single nucleotide polymorphisms. In some cases, alterations explicitly modified the expression motifs described for these operons, such as the promoter boxes, operators, and Shine-Dalgarno sequences. In addition, changes in DNA curvature and mRNA secondary structures, which are structural elements that regulate expression, were also calculated. According to their influence on RND upregulation, the catalog of upstream modifications were associated with "experimentally verified," "presumed," and "probably irrelevant" degrees of certainty. For experimental verification, DNA of upstream sequences independently carrying selected markers, three for each RND operon, were fused to a luciferase reporter plasmid system. Five out of the nine selected markers tested showed significant increases in expression with respect to the wild-type sequence control. In particular, a 25-fold expression increase was observed with the ISAba1 insertion sequence upstream the adeABC pump. Next, overexpression of each of the three multi-specific RND pumps was linked to their respective antibacterial substrates by a deep A. baumannii literature screen. Consequently, a data flow framework was then developed to link genomic upregulatory RND determinants to potential antibiotic resistance. Assignment of potential increases in minimal inhibitory concentrations at the "experimentally verified" level was permitted for 42 isolates to 7-8 unrelated antibacterial agents including tigecycline, which is overlooked by conventional resistome predictors. Thus, our protocol may represent a time-saving filter step prior to laborious confirmation experiments for efflux-driven resistance. Altogether, a computational-experimental pipeline containing all components required for identifying the upstream regulatory resistome is proposed. This schema may provide the foundational stone for the elaboration of tools approaching antibiotic efflux that complement routine resistome predictors for preventing antimicrobial therapy failure against difficult-to-threat bacteria.

Project description:Transporters belonging to the chromosomally encoded resistance-nodulation-division (RND) superfamily mediate multidrug resistance in Gram-negative bacteria. However, the cotransfer of large gene clusters encoding RND-type pumps from the chromosome to a plasmid appears infrequent, and no plasmid-mediated RND efflux pump gene cluster has yet been found to confer resistance to tigecycline. Here, we identified a novel RND efflux pump gene cluster, designated tmexCD1-toprJ1, on plasmids from five pandrug-resistant Klebsiella pneumoniae isolates of animal origin. TMexCD1-TOprJ1 increased (by 4- to 32-fold) the MICs of tetracyclines (including tigecycline and eravacycline), quinolones, cephalosporins, and aminoglycosides for K.pneumoniae, Escherichia coli, and Salmonella TMexCD1-TOprJ1 is closely related (64.5% to 77.8% amino acid identity) to the MexCD-OprJ efflux pump encoded on the chromosome of Pseudomonas aeruginosa In an IncFIA plasmid, pHNAH8I, the tmexCD1-toprJ1 gene cluster lies adjacent to two genes encoding site-specific integrases, which may have been responsible for its acquisition. Expression of TMexCD1-TOprJ1 in E. coli resulted in increased tigecycline efflux and in K. pneumoniae negated the efficacy of tigecycline in an in vivo infection model. Expression of TMexCD1-TOprJ1 reduced the growth of E. coli and Salmonella but not K. pneumoniaetmexCD1-toprJ1-positive Enterobacteriaceae isolates were rare in humans (0.08%) but more common in chicken fecal (14.3%) and retail meat (3.4%) samples. Plasmid-borne tmexCD1-toprJ1-like gene clusters were identified in sequences in GenBank from Enterobacteriaceae and Pseudomonas strains from multiple continents. The possibility of further global dissemination of the tmexCD1-toprJ1 gene cluster and its analogues in Enterobacteriaceae via plasmids may be an important consideration for public health planning.IMPORTANCE In an era of increasing concerns about antimicrobial resistance, tigecycline is likely to have a critically important role in the treatment of carbapenem-resistant Enterobacteriaceae, the most problematic pathogens in human clinical settings-especially carbapenem-resistant K.pneumoniae Here, we identified a new plasmid-borne RND-type tigecycline resistance determinant, TMexCD1-TOprJ1, which is widespread among K. pneumoniae isolates from food animals. tmexCD1-toprJ1 appears to have originated from the chromosome of a Pseudomonas species and may have been transferred onto plasmids by adjacent site-specific integrases. Although tmexCD1-toprJ1 still appears to be rare in human clinical isolates, considering the transferability of the tmexCD1-toprJ1 gene cluster and the broad substrate spectrum of TMexCD1-TOprJ1, further dissemination of this mobile tigecycline resistance determinant is possible. Therefore, from a "One Health" perspective, measures are urgently needed to monitor and control its further spread. The current low prevalence in human clinical isolates provides a precious time window to design and implement measures to tackle this.

Dataset Information

AdeIJK, a resistance-nodulation-cell division pump effluxing multiple antibiotics in Acinetobacter baumannii.

Publications

AdeIJK, a resistance-nodulation-cell division pump effluxing multiple antibiotics in Acinetobacter baumannii.

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